Principles of Color Television
Three Basic Colors of Television
• Blue
• Red
• Green
11 %
30%
59 %
Three Color Characteristics
• Hue – adjusted color sometime called tint control (from green to red)
• Brightness – illumination of the picture that includes sharpness of edges including the contrast control
• Saturation -
Lights
• 430 Terahertz (430 X 10 Hz) to 750 Terahertz (750 X 10 Hz)
• 430 Terahertz is considered as a wavelength• 750 Terahertz correspond to the color red and
the higher frequency• 400 nm seen deep blue• Some colors do not correspond to any one given
wavelength of light (example brown and purple)
12
12
Electromagnetic Spectrum
Color Mixing
• When sunlight passes through a glass prism will separate into multitude of color components. The display is called saturation
Subtractive color mixing
• Subtractive mixing – make use of filtering action that dyes pigments and inks. Ex: pictures, photographs, color movies.
• Additive mixing – superior to subtractive mixing. Using the primary colors as the base.
Spectrum of White light
Additive Mixing
Result of Additive Mixing
Result of 3 color additive mixing
WhitePale
yellowGray pink
Pale green
BluishGreen
100%White
50%White
50 %Saturated
red
50%Saturated
Yellow
Luminance Level
• Dark yellow producing a shade of gray approaching black
• Y= 0.59G + 0.39R + 0.11B
• For equal Energy• Y = 0.59(1) + 0.30(1) + 0.11(1)
» =1.00
• For 50 % red 100% blue 100% green• Y = 0.59G + 0.30R + 0.11B
» = 0.59(1) + 0.30(1) + 0.11(1)
» = 0.59 + 0.15 + 0.11
» =0.85
Object size and color
• A 23 in television picture tube can show a video signal of 0.5 MHz or less correspond to horizontal picture tube object sizer ranging from 0.34 in or more.
• Object sizes ranging from 0.34 in to a minimum of 0.12 in corresponding to the half cycle of video frequency of 1.5 MHz.
• Only two colors orange and cyan can provide complete color reprodution
continuation
• Luminance signal information has required bandpass from 0 to 4.2 MHZ
• The narrower the bandwidth of the color information the less complex the color tv system need be.
Color Television Transmission
Matrix Y Color Transmitter
G-Y Matrix
• (R –Y) + Y = R
• (B – Y) +Y = B
• (G – Y) + Y = G
Y color Receiver
Balance Modulator
Color Burst color synchronizing
Phase relationship
• The amplitude of the composite chrominance signal represents the color Saturation information and its phase corresponds to the actual color of hue information of the picture being transmitted
• Phasor – a sine and cosine waves can be represented by a straight line.
Three phasors properties
• Length
• Speed of counter clockwise rotation
• Relative angular position
Performance of the chrominance signal
• Y =0.59G + 0.30R + 0.11B=0.599(0) +0.30(0) + 0.11(0) = 0.41
• R –Y = 0.70R – 0.11B– 0.59G=0.70(1) – 0.11(1) – 0.59(1) = 0.59
• B – Y 0.89B – 0.30R – 0.59G=0.89(1) – 0.30(1) – 0.59(0) = 0.59
COLOR PHASE ANGLE
Misconvergence
Low green adjustment
High adjustment of blue
Dominant Red missing green
Dominant Blue Missing Green
Missing Red
Too much Blue adjustment
Low red adjustment
Low green and blue adjustment
Low red and green color adjustment